For over fifteen years, laser energy has been used routinely in major and minor surgical procedures. Safety and efficacy have been proven for applications in plastic surgery, dermatology, ophthalmology, otolaryngology, neurological surgery, obstetrics and gynecology, gastroenterology, urology, and general surgery. With the development of rigid and flexible endoscopic surgical techniques, there has been parallel interest in endoscopically-guided laser surgery. In many endoscopic procedures, including arthroscopy, pathological tissue may be confined to relatively inaccessible spaces, and a laser surgery technique would greatly facilitate removal of these lesions.
There are potential advantages to utilizing laser energy for arthroscopic meniscectomy, which has become one of the most frequency performed orthopedic procedures in the United States and Canada. With conventional arthroscopic meniscectomy, the mechanical instrumentation is cumbersome in the rigid confines of the knee, and often causes scuffing or gouging of the articular cartilage. Also, the small instruments used to cut relatively dense tissue have resulted in instrument failure and breakage within the joint during the course of the procedure. Focussing a laser beam between the rigid, confining articular surfaces of the knee permits remote access to torn or degenerated meniscus tissue with a decreased risk of iatrogenic injury to the articular cartilage as seen with the rigid instruments presently employed.
Previously, injuries to and degenerative lesions of the meniscus in the knee were treated by total meniscectomy. Even suspected lesions of the meniscus frequently resulted in total meniscectomy. It has been demonstrated in long term follow-up studies of patients with total meniscectomies, that a premature incidence of degenerative arthritis in the knee occurs. This led to the development of high quality arthroscopes which provide intra-articular illumination via fiber optic light bundles permitting the resection of only the structurally damaged portions of the meniscus. The use of the laser allows for greater ease with a partial meniscectomy procedure which tries to retain a functional peripheral rim of meniscus.
The focus of most laser arthroscopy investigations has been with use of the carbon dioxide laser system. However, the inherent properties of the 10.6.mu. wavelength lasers have not allowed for development of the carbon dioxide lasers as an effective or convenient laser arthroscopic system. This wavelength cannot be readily transmitted by standard fiber optics. Instead, the system must be used with larger rigid endoscopes. The arthroscopic delivery system must be connected to the laser source through a cumbersome articulated arm which limits the surgical fields that are accessible for treatment. However, experiments have been performed to show that a Nd:YAG laser can be coupled through a fiber optic cable to perform laser surgery on a meniscus.
A significant disadvantage of the carbon dioxide laser for meniscectomy is that its wavelength is not readily transmitted via optical fiber; and since it is readily absorbed by water the surgeon must use gas distention of the joint rather than the safer saline infusion procedure. During a conventional arthroscopic procedure, the joint is distended with a saline solution. All instrumentation and viewing systems are adapted to the fluid environment. Thus, the need to distend the joint with gas for the CO.sub.2 laser creates an array of complications and reduces the attractiveness of this laser to the physician. In a gaseous medium, smoking of the tissue during ablation often clouds the viewing lens and requires flushing the joint with saline. When nitrogen is employed, gas reabsorbed by the tissue during the procedure may cause swelling lasting up to one week postoperatively. In addition, maintaining distention of the joint is often difficult if several portholes are employed.
Similarly, Nd:YAG lasers have been tried to perform arthroscopic meniscectomies, but though the 1.064.mu. laser light is deliverable through standard optical fibers, the meniscus is quite transparent to the Nd:YAG wavelength and much of the energy is not absorbed. Effective ablation of meniscal tissue requires better coupling and a shorter absorption depth than is available from the Nd:YAG laser.